When constructing buildings by welding steel plates and shaped steel, the most suitable weld joint will be selected by considering the condition and the intended purpose of the welded structure. For instance, when welding two steel plates side by side at their ends, a lap joint will be selected, and when welding one steel plate to the other at right angles, a T-joint will be selected. In these joints, V-bevels or X-bevels will be made at the welding side of the steel plates to accommodate the welding medium.
A V-bevel has a face (called a root face) which is perpendicular (vertical) to the surface of the steel plate, and above this root face the bevel is made which has a certain depth and angle with respect to the surface of the plate, (see FIG. 2). An X-bevel has a root face in the middle of the steel plate thickness and bevels are made above and below the root face, (see FIG. 2). The bevel angle and bevel depth will be predetermined by such welding conditions as the thickness and material of the steel plate, the welding method chosen, and so on.
A steel plate having a V-bevel or an X-bevel at one side is usually cut off from a steel material which has a larger size but the same thickness as the steel plate by using a cutting device having a gas torch for cutting the root face and a gas torch for cutting the bevel face. When cutting the steel plate from the steel material, the cutting size and the cutting shape are set in advance. The cutting size and shape are determined by the dimensions and location of the root face.
U.S. Pat. No. 4,205,828 to Hooper discloses cutting the side of a steel plate aslant. This patent describes vertical (root face) cutting and slant (bevel) cutting one after the other. Namely, Hooper teaches to cut the edge of the steel plate twice with a single torch. Thus, the Hooper cutting device only cuts the root face or the bevel at one time, and it cannot make a V-bevel or an X-bevel at the end of the steel plate in one operation.
In Hooper, the mechanism to incline the torch comprises a cylinder moved by liquid pressure, which rotates a lever, and following its rotation, the torch is inclined. Thus, it is impossible for the device to finely control the angle of the torch to match it to the angle of the desired bevel.
On the other hand, a known bevel cutting device to cut an X-bevel or a Y-bevel has a vertical cutting torch to cut the root face and a bevel cutting torch to cut the bevels. This kind of device has an arc rail along which the bevel torch inclines at a right angle to a direction of the torch's cutting direction, and a shifting means to move the torch at a right angle to the torch's cutting direction. This kind of cutting device is usually set on a cross-shifting stand which is loaded on a moving stand running along the lengthwise direction of steel material. The vertical cutting torch and the bevel cutting torch cut plates according to data set up in advance (e.g., entered into a numerically controlled cutting device) by controlling the moving stand and the cross-shifting stand along the root face.
The arc rail has a rack along all of its range. A holder for supporting the bevel cutting torch has a motor to set the angle of the beveling, and the motor is attached to the rack with a pinion. By driving the motor to rotate the pinion, the bevel cutting torch and its holder move along the arc rail, and then the bevel cutting torch can be inclined to the desired angle.
The shifting means is constructed so as to avoid interference between the vertical cutting torch and the bevel cutting torch by shifting the arc rail in the side direction of the cross-shifting stand (i.e., perpendicular to the plate-cutting direction).
With this known bevel cutting device, the rack of the arc rail and the pinion are exposed to the working environment of the gas-cutting equipment. Therefore, iron powder, dust, and other debris produced by the cutting equipment easily adhere to the rack and the pinion and obstruct the smooth gearing thereof. For example, if iron powder sticks between the rack and the pinion causing a gearing problem, this will obstruct the smooth moving of the bevel cutting torch and make it impossible to precisely incline the torch at the desired angle.
For this reason, the known bevel cutting device needs frequent maintenance to keep the device in good working condition. This creates problems like a decline of work efficiency and difficulty in operation.